I have a cheap case wrench...

an Indian knock-off of the expensive one. It's a three-point type with different heads that you can put in depending on the type of caseback you're removing. Works fine, just take your time and go slowly when using it.

I also have one of those rubber balls, while they might not remove a super tight case back, they do work, and are also useful once you've cracked the back intially and then use the ball to remove the caseback the rest of the way, with no worries about scratching anything.